This invention relates to a thrust-setting system for a gas turbine engine and, more particularly, to an electronic control for setting the thrust in such an engine.
One of the main functions of an engine control system is to provide for the generation of that specific level of thrust required or demanded by the throttle position set by the pilot. Such a system, in order to insure that actual thrust corresponds to demanded thrust, must have a source of information respecting the actual thrust output of the engine. Since it is extremely impractical to provide a direct thrust measurement, a thrust-indicating parameter such as fan speed or engine pressure ratio, which is directly related to thrust, may be used as a proper source of information.
In modern-day gas turbine engines it is important that the reliability of the above-described thrust-setting system be quite high since failure of the systems may result in severe consequences. Prior art approaches to providing increased reliability have been varied and have included the utilization of secondary thrust-setting systems, which are normally inoperative and completely independent of a primary system, as a back-up system in the instance of failure of the primary system. These duplicative systems have proved to be expensive, especially with duplication of the complex and extensive control circuits normally associated with aircraft gas turbine engines. Moreover these secondary systems known in the prior art serve no useful function while the primary system is operative and hence the aforementioned expense is incurred on a secondary system that performs no useful benefit during most of the operating life of the gas turbine engine.